During processing semi-conductor wafers are subjected to numerous process steps in various machines and at various locations. The wafers must be transported from workstation to workstation and from facility to facility to accomplish these various steps. Numerous types of shipping devices are known for handling storing and shipping semi-conductor wafers. In general, such devices hold the wafers in axially aligned arrays. Where wafers are shipped from facility to facility the wafers may be exposed to sunlight for significant periods of time. Sunlight includes substantial amounts of electromagnetic radiation in the ultraviolet wavelengths. Wafer containers may also be exposed to ultraviolet light from other sources.
Current, state of the art, semi-conductor lithography production processes use deep ultraviolet lasers to image circuits with critical features ranging in size as small as one hundred thirty to one hundred fifty nanometers. It is expected that in the near future critical features may shrink to a size range of about seventy nanometers.
In the production process wafers are spin coated with a photoresist. The photoresist is then baked to adhere it to the wafer. Next, an image of the desired circuitry is projected onto the wafer using electromagnetic radiation. Today, this is commonly deep ultraviolet radiation from a laser. The photoresist material is chemically altered by exposure to ultraviolet light to create either a negative or positive image of the circuit depending on the process used. The undesired photoresist material is then etched away leaving an integrated circuit pattern on the wafer.
As discussed above, photoresists that are used in semi-conductor processes are sensitive to light in the ultraviolet wavelengths. Because of the tiny size of the critical elements of modern integrated circuits only a very small exposure to uncontrolled ultraviolet radiation can lead to spoilage of a wafer. Consequently, it is desirable, in the production process, that photoresists only be exposed to the ultraviolet wave lengths of light under carefully controlled conditions. Unintended exposure will destroy the usability of wafers exposed.
Thus, wafer shipping containers used in the handling, storing and shipping of wafers are made of materials, typically plastics, that block ultraviolet light to prevent it from affecting wafers coated with photoresist material. It is also desirable that wafer shipping containers be, at least partially transparent to visible light to allow workers to determine whether a shipping container is empty or full. Thus, shipping containers have been made of materials that are transparent, at least in part, to visible light but that are relatively opaque to ultraviolet light.
Nonetheless, ultraviolet blocking is never absolute and it is desirable to expose wafer containers to ultraviolet radiation as little as possible. Thus, it would be a benefit to the semiconductor industry if wafer containers themselves could signal to workers that the wafer container was currently exposed to ultraviolet radiation. This would signal the worker to move the wafer container to an ultraviolet sheltered location.
Additionally, similar issues exist with regard to the storage and processing the disks for computer hard drives and the reticles for the lithography operations.